Apparatus for coating paper



April 27, 1954 Filed Feb. 5, 1949 w. .1. MONTGOMERY |-:-r AL APPARATUSFOR COATING PAPER 3 She ets-Sheet 1 INVENTO S William J. Montgomery BY IWilliu P.Tylor A ORNEY APrll 1954 w. J. MONTGOMERY ET AL 3 APPARATUS FORCOATING PAPER Filed Feb. 5, 1949 3 Sheets-Sheet 2 4 INVENTORS William J.Montgomery .BYfilgggjToylor ATT NE7Y( 7 w. J. MONTGOMERY ETAL 2,676,563

APPARATUS FOR COATING PAPER April 27, 1954 5 Sheets-Sheet 5 Filed Febv 51949 ontgofnery P. Taylor m JAM E mmum w Patented Apr. 27, 1954Hamilton, Ohio, assignors to The c amp fl Paper and Fibre Company,Hamilton, Ohio, a

corporation of Ohio Application February 5, 1949, Serial No. 74,766

8 Claims. l

Ihe present invention relates to apparatusfor coating paper.

In recent years a considerable proportion of the paper made for paintingpurposes has been coated with some composition of. pigment and adhesivein order to-give the paper an improved printing surface. Such coatingshave commonly been applied to paper for this-purpose, by one or theother of two well-known processes. In one of these processes the coatingmaterial is applied to the surface of the paper web and is then spreador smoothed into a smooth-surfaced layer of-the required dry weight byany of a variety of instrumentalities such as brushes, rollers, airjets, etc, the smoothing and/or spreading action being in some .casesaccompanied by removal of surplus coating material which in those casesis applied to the paper in excess of the amount required to give a-layerof the desired dry weight. The coated paper is then dried .andcalendered in a customary manner.

In the other-of these well-known processes, .a layer of coating materialis formed on the surface of an applicator roll and -isthen transferredto the surface ofa travelling paper web as a layer of the same dryweigh-tand the same degree of-nni-formity found in the coatmg on thefin.- ishedpaper. The coated paper then dried without any smoothingoperation, without removal of any of the applied coating, and withoutany other treatment. carried out subsequent to application of thecoating to the surface of the paper.

This second-named process, as commonly used, is roughly analogousto thatby which ink is fed, distributed and printed onto a paper web by .arotary press when printing a solid color. In this process, coatingmaterial, usually having a solids content of about fifty per cent, isfed by a suitable fountain, the exact. amount to be applied to thepaper, to a series of distributor rolls and by them is worked out andapplied as a thin film to -an applicator which in turn transfer-s orfprin'ts this film. onto the surface of the paper.

One object of the present invention is ..to provide in said-second-namedprocess, improvements in apparatus which shall make possiblesuccessf-uluse of a wide varietyof coating. compositions comprising pigment and:adhesive, and which shall largely counteract the strong .tendency ofcertain types of coating compositionsfito form ridges or stipples in thecoated surface of the paper, when applied thereto by said process.Another object of the invention is to provide 2 apparatus in which bits.of coating. material and/or foreign matter shall be prevented frombeing carried around on the surface of the applicator roll to leaverecurrent defects in the coated. surface of the paper. Still anotherobject is the provision of means and methods for accurately controllingand maintaining the thicknessof the coating film at all points acrossthe width .of' the web. A related object is the pro.- vision of. suchmeans which shall be independent of any sagging of, or crown or othervariations in diameter .of, any .of the rolls used. A further object isthe provision of a method and an apparatus adapted to apply coatingcompositions of higher sol-ids content and/or higher viscosity thancustomarily used. A still further object is the-simplification ofapparatus over those previously available for the application to amoving paper web of a preformed film of coating comprising pigment andadhesive. Other objects and advantages of the invention will be apparout:from the followingv more detailed description.

The present invention involves the use of novel means in order to formon the surface of an applicator roll for transfer to the paper Web, afilm of coating material of accurately controlled thickness throughout,and substantially free from ridges, sti-pples, and the like.

In accordance with the present invention and in contrast to the priorart, no attempt is made either to apply the coating material to theapplicator roll in the exact amount required for transfer to the paperor to apply it as a uniformly thick. or smooth surfaced film, Instead,it is applied in excess and without regard for uniformity or smoothnessof application, direct- 1y to the surface .of. the applicator roll. Thesurplus coating material, over and above that required for applicationof the desired amount to the paper web, is. then removed from thesurface of the. applicator roll and the residual film of coatingmaterial is smoothed out intoa condition of substantially uni-formthickness and freedom from rid e rstipp s. nd t e lik y a backwardwiping action. We have now discov-- ered that, by carrying out thiswiping action as hereinafter described, we are able to dislodge. andremove from the surface of the applicator roll any adherent hits ofcoating material or foreign matter before they have opportunity to leaverecurrent marks on the coated surface of the paper. By :this same wipingaction we are also able :to prevent accumulation of coating material onthe roll beyond the edges-oi the web, whe

it is not continuously carried away by the paper.

The preferred instrumentality for accomplishing this wiping action is arotating doctor which is pressed firmly and uniformly against the rubberor rubber-like surface of the applicator roll. This doctor, particularlywhen rotating counterdirectionally, is preferably wiped at eachrevolution, thereby preventing coating material removed from the surfaceof the applicator roll from being carried around the doctor andredeposited on the surface of the applicator. We have found that we cansubstantially eliminate all visible ridges, stipples, etc. from thecoating film by making the rotating doctor of small diameter, but thatwhen such a small diameter rotating doctor is of any substantial lengthit can only be made effective to leave a film of uniform thickness onthe applicator roll by supporting it throughout its working length,against deflection. A support for this purpose, if of suitable form,will, we find, also serve to accomplish the abovedescribed Wiping of thedoctor at each revolution thereof.

The means for applying the excess of coating material to the surface ofthe applicator roll can be varied as desired and in accordance with thetype of coating composition to be applied. The means which is adaptableto a wider variety of coating compositions than any other we have tried,comprises two rolls closely spaced in a predominantly horizontaldirection so that a pool of coating material can b maintained in the nipbetween them, one of said rolls being substantially in contact with theapplicator roll. Said rolls are advantageously rotated at speedsdifferentially controlled in such manner that there is a continuous moreor less violent agitation of the coating material in the nip, and thatthe one roll continuously withdraws a metered excess of coating materialfrom the pool and transfers it to the surface of the applicator roll.

One embodiment of the invention will be further described with referenceto the accompanying drawing, in which:

Figure 1 is a diagrammatic elevational view of a coating device forapplying coating material to one side of a paper web in accordance withthe present invention.

Figure 2 is a similar diagrammatic view of a coating device for applyingcoating material simultaneously to both sides of a paper web, inaccordance with the present invention.

Figure 3 is a detail showing means of adjusting the fountain rolls.

Figure 4 is a diagrammatic view showing means for rotating the rolls andfor mounting and driving the rotating doctor.

Figure 5 is a detail view to a considerably larger scale, showing, insection partly taken on line 5--5 of Figure 6, th rotating doctor, thesupporting and adjusting devices therefor, and the relationship of thedoctor to the surface of the applicator roll. V

Figure 6 is a fragmentary'detail showing a portion of the rotatingdoctor and its flexible support.

Figures 7 and 8 are diagrammatic views to a much smaller scale, showingthe application of coating in accordance with the present invention as apart of the papermaking operation on the paper machine.

One illustrative embodiment of the present invention is shown in Figure1 in which the paper web 2| is moving in the direction indicated by thearrow and is passing, and being lightly and and absolute speeds of therolls, etc.

advantageously adjustably pressed, between the applicator roll 22 withits surface layer 23 of semi-soft rubber or rubber-like material and thebacking roll 24, which may if desired be provided with a similar surfacelayer 25. The most advantageous hardness of surface layer 23 has ingeneral been found between densities ,of about 60 and 150 as measured bythe Pusey and Jones plastometer (using a inch ball), and has morefrequently been found between and on the same scale.

A pool 26 of coating material, supplied through a pipe 21, is maintainedin the nip between rolls 30 and 3| which rotate at controlleddifferential speeds in the directions indicated by arrows in thedrawing.- If needed to prevent the coating in pool 26 from overflowingat the ends of the rolls, end dams (not shown) of any suitable type mayb provided, as is well understood in the art. These rolls are spacedclosely together and the spacing between them is regulated to controlthe amount of coating material carried through the nip by eachrevolution of roll 3| for transfer to applicator roll 22. Thisregulation'of the spacing may be accomplished, as illustrated in Figur3, by means of a screw 32 at each end of rolls 3! 3|, which may ifdesired be provided with a micrometer dial 33. Each screw 32 serves toadjust the position of a wedge 34 between bearing blocks 36 and 31 inwhich are journaled rolls 30 and 3| respectively. A spring 35 serves tohold bearing block 36 against wedge 34 and thus maintain the width ofnip between rolls 30 and 3| at the setting for which it is adjusted.Spring 35 also serves as a safety device to prevent damage in case someforeign object should get between the rolls.

Roll 3| is herein described as being substantially in contact with therubber or rubber-like surface 23 of applicator roll 22. This term isused in the present specification and claims to define the degree ofcontact required to pass through the nip and apply to the surface 23 ofroll 22, the desired excess of coating material. The degree of contactrequired for this purpose depends on a number of factors such as theamount of coating material to be transferred, the viscosity and flowproperties of the specific coating material being applied, the hardnessor softness of th rubber-like cover 23, the relative It may vary from aslight positive spacing or clearance to a slight negative spacing suchthat the metallic roll 3| slightly indents the yielding resilientsurfacev of the cover 23 on roll 22. An adjustable degree of contactbetween rolls 22 and 3| is accordingly advantageous as is also theability to remove roll 3| from contact with roll 22 when desired. Theadjustment may be made by an adjustable wedge 38 at each side of themachine, in the manner described for adjusting the spacing betweenrolls30 and 3|. The fountain roll-carrying structure 39 is illustrated inFigure 3 as held against wedge 38 or withdrawn therefrom toseparaterolls 3| and 22 by any suitable means such as hydraulic cylinder 4!). Inpractice it is not necessary-to,-

know whether there is positive clearance, contact without pressure, or adefinite indentation of rubber surface 23 by the roll 3|. It is onlynecessary to see that wedges 38 are so adjusted thatace-aces thicknessrequired for transfer of the specified dry weight of coating to thesurface of the paper web.

Means by which rolls 22, 30, and 3| may be driven is illustrated moreparticularly in Figure 4. The roll 22 is driven at a surface speedsubstantially equal to paper speed (which may vary in different machinesfrom. less than 100 to more than 1000 feet per minute) by any suitablemeans such as a sprocket 4|, chain 42, and sprocket 43, which may be onthe output shaft of a speed reducer 44, the input shaft 45 of which isdriven at a speed which advantageously may be adjusted slightly withreference to the speed of the paper customary between different elementsin papermaking machines. This slight speed adjustment may beaccomplished in any manner desired, as

for example by the conventional cone pulley '45 and belt 41 which isdriven from another cone pulley (not shown) which may be on the maindrive shaftof the machine.

The rolls 30 and 3| are advantageously geared together, as by gears 50and 5|, in any desired speed ratio, as for example 1 to 2, or 2 to 3.Rouse may be conveniently driven from roll 22 by any suitable means suchas sprocket 52, chain 53, variable speed device 54, chain 55, andsprocket 56. In cases where speed adjustment between rolls 22 and Bi isnot desired, the variable speed device 54 may be omitted and chain 53-passed directly from sprocket 52 to sprocket 56 as indicated in Figurev1. The actual speeds of these rolls do not appear to be critical, butpermit of wide variation. We have, for example, successfully used asurface speed. equal to paper speed, for roll 22; two-thirds of thisspeed for roll 3|; and from one-third to one-half paper speed for roll30.

The surface speed of roll 22 should be substantially the same as thepaper speed. It may be observed, however, that due to a slightdeformation of the rubber covering 23 by contact with roll 24 and aconsequent indeterminate elongation of the surface of roll 22 where itis in contact with the paper web 2|, the actual exact surface speedatthat point is unknown. In practice, however, this is a matter of noconcern since it is only necessary to adjust the speed, as by shiftingbelt 4! on cone pulley 46, to provide the proper draw on the paper web,in the manner familiar to operators of paper machinery.

The surface speed of roll 3| may vary from a minimum which is justadequate to carry a sufficient excess of coating material from pool 25to the surface of roll 22 without opening the nip between rolls 33 and3! sufiiciently to permit drainage of pool 25, up to a speed equal to orgreater than that of the roll 22. When the paper speed is high, thesurface speed of roll 3| is advantageously materially less than paperspeed. The surface speed of roll is advantageously materially differentfrom and usually less than that of roll 3| in order to provide shear onthe coating material as it passes through the nip. Furthermore, it iswell known that a standing body of coating material of the types usedfor the present purposes should, in general, be continuously agitated.We have now discovered that by increasing the surfac speeds up to theorder of 300 feet per minute or more, the rotationof rolls 3!! and 3| isitself usually adequate to provide all of the agitation normally neededin the pool 25.

The means by which the surplus coating material is removed from thesurface23 of roll 22 is most clearly shown in Figures 4, 5, and 6. Thismeans comprises av rotating doctor 6| which advantageously rotatescounterdirectionally as indicated by the arrow in Figure 5. It ispreferably formed of a corrosion-resistant and wearresistant materialsuch, for example, as chromium-plated steel or any of the suitable knownalloys containing material proportions of chromium, nickel, cobalt,tungsten, molybdenum, or similar hard and corrosion resistant alloyingelements. It is. held throughout its working length against deflectionby any suitable means such as the split support 62 which may be made oflaminated phenolic resin, corrosion resistant metal, or other suitablematerial. The support 62 is held in place on a rigid mounting bar 63 bya cover plate 64 and a plurality of screws 65. The doctor 6| is adjustedinto the desired degree of contact with the surface 23 of roll 22 byadjusting screws 66, which are threaded through a flange 61 on the bar63 and press against the support '62 for doctor 6|.

Even when the doctor 6| is perfectly straight, differences in coatingthickness have been found to occur across the width of the paper web,particularly when this width isv as great as that of many modernpapermaking machines. These have generally been found to be caused bycorresponding differences in pressure or degree of contact betweendoctor 6| and the rubber surface 23 of roll 22 along the length of theseparts. Such differences in pressure may be due to any of a variety ofcauses such as sagging of roll 22, a crown on its surface, or othervariation in diameter along its length, soft or worn portions of cover23, or the like. We have now found it possible to compensate for anysuch unevenness and secure coatings of uniform thickness (or whendesired, of any specified variation in thickness) across the width ofthe paper web, by locally adjusting the doctor iii to give it therequired pressure on, or degree of contact with, rubber surface 23 onroll 22, at suitable intervals along its working length. In order tomake possible this local adjustment, the support 62 for doctor 5| isrendered flexible as by providing slots H which reach almost to thedoctor 6| at suitably close intervals throughout its length. Theadjustment is then made by means of the necessary number of suitablyspaced adjusting screws 65. To permit this adjustment, the holes l2through which clamp screws 65 extend, are suitably slotted as indicatedin Figures 5 and 6.

In order that the device shall function properly in uniformly wiping offsurplus coating material l5 and smoothing the remaining film l5, and indislodging any bits of coating material or foreign matter which mayadhere to surface 23,

the rotating doctor 6| must be pressed with av firm but light andregulatabie pressure against the rubber or rubber-like surface 23 onroll 22. Because of the yielding nature of the surfacing material 23 onroll 22, this pressure causes the rotating doctor 6| to indent thesurface 23 to a greater or lesser extent as indicated at in Figure 5.This pressure may be applied by any of the known methods such asweights, springs, hydraulic devices, etc., but for purposes ofillustration the mounting bar 63 which carries support 62 for doctor 5|,is shown in Figure 4. as arranged to swing around a fixed pivot 3| andto be pressed against cover 23 of roll22- byadjustable; weights 82slidably mounted on arms 83 which are rigidly attached to the oppositeends of mounting bar 63. The actual degree of pressure to be useddepends on a variety of factors such as the diameter of the doctor 6|,the density of the rubber cover 23 on roll 22, the speed of operation,the viscosity of the coating material used, and the weight of coating tobe applied. When using doctors of from inch to one inch in diameter andrubber coverings of the specified density on roll 22 at speeds of theorder of 600 feet per minute, pressures of from one to four pounds perlinear inch have usually been found satisfactory, though greater orlesser pressures may be desirable under specific circumstances. We have,for example, applied about nine pounds, dry weight, of coating per ream(500 sheets 25 x 38 inches) by using a pressure of about two pounds perlinear inch on a M; inch diameter doctor pressing against a rubber rollsurface having a density of about 110 (P. 8: J.) when using a coatingcomposition of about 62% solids at a viscosity of about 8 poises.

Rotation of the doctor 6| may conveniently be secured by meansindependent of that for rotating rolls 22, 3|], and 3|. Convenient forthis purpose is a geared-head motor 85 mounted on an extension of one ofthe arms 83 and operatively connected by chain 86 to a sprocket 81 whichis in turn operatively connected to the end of doctor 6|. In most caseswe prefer to rotate this doctor in a direction counter to the directionof travel of the roll surface thereunder, as indicated in Figure 5,though it may if desired be rotated co-directionally with the rollsurface since, because of its slow surface speed, a change in directionof rotation makes little difference in relative speeds of applicator anddoctor. The backward wiping action by which the surplus coating materialis removed from the applicator is thus accomplished regardless ofdirection of rotation of the doctor. The speed of rotation of doctor 6|is not critical. It needs to be great enough to prevent lodgement ofdirt or coating lumps and is advantageously low enough to avoid throwingof the coating and undue wear on the parts. We have also found, whenrotating doctor 6| counterdirectionally, that the useful life of doctorholder 62 can be greatly increased by making the surface speed of thedoctor 6| very slow in relation to the speed of the paper. This not onlymeans fewer revolutions of the doctor and therefore less wear on theholder, but it also means that any reasonable amount of coating materialwhich leaks around doctor 6! due to.

wear of holder 62 and is redeposited on the surface 23 of applicatorroll '22, becomes spread so thinly thereover that it cannot be detectedafter being transferred to the surface of the paper. With a doctor offrom ot one inch in diameter, speeds of from 5 to 60 R. P. M. have beenfound to give satisfactory results, though we normally prefer speeds inthe lower portion of this range. However, in appropriate circumstances,speeds above or below the stated range may be used.

The doctor 6| may be of any desired diameter from a minimum of about ,4;inch up to several inches or more. The smallest diameters are difficultto use successfully because of the difliculty in securing sufiicientlylight and even pressures to prevent undue indentation of the rubbercover 23 on roll 22, whereas the larger diameters rewise desired, inorder to limit the coating weight to the degree commonly required. Alsolocal adjustment of the doctor 6| by the screws 66 becomes moredifficult as the diameter increases. For these reasons we generallyprefer to use doctors between inch and 1% inches in diameter. We havefound %'inch diameter suitabl for use when roll 22 has a rubber covering23 with a density of about 0 as measured by the Pusey & Jonesplastometer. Accordingly, the term small diameter" is used in thepresent specification and claims to define a diameter of the rotatingdoctor of not over about l inches, and will in general be understood notto refer to diameters of less than A; inch.

The term "rubber as used in the present specification and claims withreference to the covering 23 on applicator roll 22, is to be understoodas including compositions of suitable synthetic rubber-like materials aswell as compositions of natural rubber.

If it is desired to coat both sides of the paper simultaneously, it isonly necessary to duplicate the above-described apparatus above the webas shown in Figure 2, in accordance with which coating material isapplied in excess to the rubber or rubber-like surface 25 of roll 24 bythe rolls 30 and HI. The excess is then removed and theremaining film ofcoating material is leveled and smoothed by rotating doctor GI in themanner already described. The means for driving and controlling thespeeds of the rolls 24, |30, and |3|, and for rotating the doctor |6|,are advantageously identical with the means illustrated in Figure 4, inwhich they are viewed from the end of the rolls opposite to that fromwhich these rolls are viewed in Figure 2.

The coating device described can be used to coat paper either in orapart from the papermaking machine. value as a part of a papermakingmachine. One such arrangement of the device is illustrateddiagrammatically in Figure 7. The paper after at least partial drying ondriers 9!, passes between the coating rolls 22 and 24, as described, andthe coated web 2| then passes on and around another set of driers 92 andafter drying passes to calenders, reels, etc. (not shown) in the usualmanner.

If desired, the paper web 2| can be passed through a calender 53 afterit leaves driers SI and before it passes between coating rolls 22 and24, as illustrated in Figure 8.

Although the application of the excess of a wide variety of coatingmaterials to the rubber covering 23 on roll 22 (or rubber covering 25 onroll 24) is advantageously accomplished by the tworoll fountaindescribed, any other means which will continuously and dependably applyan excess of the particular coating material being used, at all pointsacross the working width of roll 22, may be used if desired.

By the process and apparatus described, We

have found it possible to apply a Wide variety of" coating compositionsto paper at paper machine speeds by a printing operation, without leav-"ing any visible sign of the ridges and stipples frequently foimd onpaper coated by the printing process, and to apply the coating in thismanner either to a dried paper web separate and apart from thepapermaking machine, or to a partially or fully dried web on thepapermaking machine itself. We have further found it possible, by themeans and methods herein described, to utilize successfully not onlysuch coating compositions as quire more fluid coatings than are oftenother- 75. have heretofore been used on printing type coat- It is,however, of particularing deviceabut also other types of coating compo.sitions which, so far as we are aware, have never been successfullyused in practice on coating devicesof that type. We have additionallyfound that comprising: a pair of rubber covered rolls, be-

tween which the paper web is lightly pressed, for applying apredetermined amount of coating to each side of the web at the sametime; means for rotating said rolls at surface speeds approximating thatof the paper web; means associated with each of said applying rolls formetering an excess of coating material onto the surfaces of therespective applying rolls; a small diameter reversely rotatingcylindrical doctor associated with each of said applying rolls forremoving the surplus coating material and smoothing the remainder into asubstantially smooth and uniform film; means for independentlysupporting and wiping each of said doctors throughout its workinglength; and independent means, acting through said supporting and wipingmeans, for holding each of said doctors against the coating film on thesurface of the corresponding applicator roll under pressure sufficientto indent the rubber surface thereof.

2. The device of claim 1 wherein said doctor supporting means anddoctors are slightly flexible and independent adjusting means isprovided for flexing each of said supporting means to flex the doctorsupported thereby to regulate the thickness of the film of coatingmaterial left on the surface of each applicator, along the Workinglength thereof, and to compensate for variations in diameter and forvariations in hardness of the rubber cover of the correspondingapplicator roll, along the length thereof.

3. In combination with a rubber-surfaced filmapplying roll in a papercoating device: a small diameter cylindrical doctor; a flexible supportwhich substantially continuously supports said doctor throughout itsWorking length and around substantially more tha half of itscircumference; means for exerting pressure on said support to press saiddoctor against and indent said roll; adjusting means for flexing saidsupport to adjust said doctor to compensate for variations in di ameterand hardness of the rubber surface of said applying roll and equalizethe pressure exerted thereon by said doctor, throughout the workinglength thereof; and means for rotating said doctor in said support.

4. In a paper coating device: a resilient surfaced film-applying roll;means for applying a meteredexcess of coating material to the surface ofsaid roll; a reversely rotating small diameter cylindrical doctor forremoving the surplus coating material from said surface and smoothingthe remaining coating into a film thereon; flexible means for supportingsaid doctor throughout its working length and around substantially morethan half its circumference,

10 whereby flexure of said supporting means correspondingly flexes saiddoctor; means, associated with said supporting means, for continuouslywiping the surface of said doctor throughout its working length; andmeans for pressing said doctor against said surface.

5. A device for .applying coating material to a moving web of paper in apaper making machine, comprising: a rubber covered applicator roll forapplying a preformed film of coating material to the surface of themoving paper web; means for driving said applicator roll at a surfacespeed substantially the same as that of the moving paper web; means forapplying coating material to the surface of said applicator roll, inexcess of the amount required for transfer to the paper web; means forremoving the surplus coating material from the surface of saidapplicator roll and leaving on said surface a substantially uniform filmof coating material of the thickness required for transfer to thepaper'web; said means comprising a small diameter rotating cylindricaldoctor, means for supporting said doctor continuously throughout itsworking length, and means for exerting pressure on said supporting meansto press said doctor against the coating material on the surface of saidapplicator roll; said doctor supporting means being flexible andadjusting means being provided for flexing said supporting means to flexthe doctor to regulate the thickness of the film of coating materialleft on the surface of the applicator roll, along the working lengththereof, and to compensate for differences in diameter and differencesin hardness of the rubber cover of the applicator roll along the lengththereof.

6. The device of claim 5 wherein the doctor supporting means enclosesand fits closely around said doctor throughout substantially more thanhalf of its circumference and leaves exposed that portion of the doctorsurface which is adjacent the applicator roll.

'7. A device for applying coating material to a moving web of paper in.a paper making machine by continuous transfer of a preformed film ofcoating material to the moving paper Web from a rubber surfacedapplicator roll rotating at a surface speed approximately equal to thatof the moving web, the combination with the rubber surfaced applicatorroll of means for continuously applying to its surface a film of coatingmaterial of metered, substantially uniform thickness, materially greaterthan the thickness required for transfer to the surface of the paperweb, and means for removing the excess coating material from said filmto reduce said film to the thickness required for transfer to the paperweb and leave it smooth and of substantially uniform thickness; saidmeans for removing the excess coating, from the film metered onto thesurface of the applicator roll, comprising: a small diameter cylindricaldoctor; means for rotating said doctor in a direction reverse to that ofthe applicator roll surface adjacent thereto; means for supporting saiddoctor continuously throughout its length; wiping means, continuousthroughout the working length of said doctor, for continuously wipingcoating material from said doctor during its rotation; and means forholding said doctor against the coating film on the surface of saidapplicator under pressure sufficient to indent the rubber surface ofsaid applicator.

8. A device for applying coating material to a moving web of paper in apaper making machine by continuous transfer of a preformed film ofcoating material to the moving paper web from a rubber surfacedapplicator roll rotating at a surface speed approximately equal to thatof the moving web, the combination with the rubber surfaced applicatorroll of means for continuously applying to its surface a film of coatingmaterial of metered, substantially uniform thickness, materially greaterthan the thickness required for transfer to the surface of the paperweb, and means for removing the excess coating material from said filmto reduce said film to the thickness required for transfer to the paperweb and leave it smooth and of substantially uniform thickness; saidmeans for removing the excess coating from the film metered onto thesurface of the applicator roll, comprising: a small diameter reverselyrotating cylindrical doctor; flexible means for supporting said doctorcontinuously throughout its working length; means for continuouslywiping said doctor throughout its working length, as it rotates; meansfor holding said doctor against the coating film on the surface 12 ofsaid applicator under pressure sufllcient to indent the rubber surfaceof said applicator; and means for flexing said supporting means tocompensate for variations in diameter or hardness of the rubber surfaceof said applicator, along its length.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,312,034 Jones Aug. 5, 1919 1,661,174 Francis Mar. 6, 19281,921,369 Massey Aug. 8, 1933 2,214,787 Dickhaut et a1 Sept. 17, 19402,243,604 Parkinson May 27, 1941 2,334,102 Kauppi et al Nov. 9, 19432,369,378 'I'hiele et al. Feb. 13, 1945 2,398,844 Muggleton et al. Apr.23, 1946 2,406,057 Barrett et a1 Aug. 20, 1946 2,560,572

Haywood et al July 17, 1951

